Versions 2.0.10 of Mosquitto has been released. This is a security and bugfix release.


  • CVE-2021-28166: If an authenticated client connected with MQTT v5 sent a malformed CONNACK message to the broker a NULL pointer dereference occurred, most likely resulting in a segfault. This will be updated with the CVE number when it is assigned. Affects versions 2.0.0 to 2.0.9 inclusive.


  • Don't overwrite new receive-maximum if a v5 client connects and takes over an old session. Closes #2134.
  • Fix CVE-2021-28166. Closes #2163.


  • Set receive-maximum to not exceed the -C message count in mosquitto_sub and mosquitto_rr, to avoid potentially lost messages. Closes #2134.
  • Fix TLS-PSK mode not working with port 8883. Closes #2152.

Client library

  • Fix possible socket leak. This would occur if a client was using mosquitto_loop_start(), then if the connection failed due to the remote server being inaccessible they called mosquitto_loop_stop(, true) and recreated the mosquitto object.


  • A variety of minor build related fixes, like functions not having previous declarations.
  • Fix CMake cross compile builds not finding opensslconf.h. Closes #2160.
  • Fix build on Solaris non-sparc. Closes #2136.